1. Field of the Invention
The invention is directed to a polymerization process and a catalyst system for the production of polyphenylene ethers of controlled molecular weight and structure. The invention is also directed to polyphenylene ethers made by this process having stable melt behavior, low odor and other advantageous properties, and to thermoplastic blends of these polymers with other thermoplastics, these blends also having advantageous properties.
2. Brief Description of the Prior Art
The polyphenylene ethers and processes for their preparation are known in the art and described in numerous publications, including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875. Other procedures are described by Van Dort, U.S. Pat. No. 3,365,422, Bennett and Cooper, U.S. Pat. Nos. 3,639,656, 3,642,699, 3,733,299, 3,838,102, 3,661,848 and 4,092,294, and Olander, U.S. Pat. No. 4,054,553 and 4,083,828. All of these patents are incorporated herein by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst, generally a metal salt or complex, most typically a copper or manganese compound.
Many processes utilizing manganese compounds as part of the catalyst system have been proposed. Of these, most utilize a manganese compound combined with a basic compound, such as sodium hydroxide, and an amine ligand. Examples of such processes are given in Olander, U.S. Pat. Nos. 4,054,553 and 4,083,828, and by Nagaoka et al., U.S. Pat. No. 4,868,276. Systems of this type are noteworthy because of their high catalytic activity, however, the molecular weight of the polymers thus produced cannot be easily controlled. Moreover, in all of these systems, the produced polymers incorporate nitrogen from the amine ligand, giving rise to structures believed to be of the so-called Mannich type, having aminomethyl groups located ortho to the phenolic hydroxyl on end groups of the polymer chain and ortho to the oxygen in position 1 on repeating units of the polymer chain. Such structures are known to be unstable on heating, generating malodorous amines and quinone methide structures which are reactive.
If the amine ligand is omitted, the aminomethyl groups of course cannot form, but in their place, the polymer tends to have relatively unstable benzylic ether structures adjacent to the phenolic hydroxyl on chain ends and adjacent to the position 1 oxygen on repeating units in the polymer chain; this chemistry is described by White and Nye, Macromolecules 1990, 23, 1318ff. Such polymers are more branched than their counterparts made using amine ligands. Polymers of the type made without amine ligands tend to lose molecular weight and increase their polydispersity on heating, presumably due to chain scission and loss of branches. Loss of molecular weight on heating and increase of polydispersity (broadening of molecular weight distribution) is generally considered an undesirable characteristic for a thermoplastic resin, associated with decline of mechanical properties, poor flow properties during processing, problems in compatibility of blends, and difficulty of reworking scrap. The manufacture of wholly satisfactory polymers using manganese catalysts therefore has hitherto not been achieved; with amine ligands the products have had an odor problem, while without amine ligands, the products have had a thermal stability (molecular weight stability) problem.
My invention provides a process for making polyphenylene ethers which affords control over molecular weight and polymer structure. It makes available thereby new polyphenylene ethers of controlled molecular weight and structure, which exhibit stable or slightly increasing molecular weight on heating, and which have little or low amine nitrogen content and consequently little or no amine odor emissions on heating. These new polyphenylene ethers are useful in thermoplastic blends having stable flow properties and reduced odor.